<?php
/**
 * Created by PhpStorm.
 * User: User
 * Date: 2017/10/16
 * Time: 18:52
 */class DB{
     static $obk=null;
     private  function _construct(){
         echo "wo ca ";
     }
     static  function  getObj(){
         if(is_null(self::$obj)){
             self::$OBJ=NEW self();

         }
         return self::$obj;
     }
     public function select(){
         echo "select data...";
     }
}
var_dump(DB::getObj());
var_Dump(DB::getObj());